Hybrid electric vehicles (HEVs) have gained prominence in the automotive market due to a diminishing supply of fossil fuels, increased concern over greenhouse gas (GHG) emissions, and increasingly stringent governmental regulations on automobiles. The transportation sector in the United States was responsible for 33% of the GHG emissions and 71% of the petroleum usage in the country in 2012. HEVs represent a pragmatic solution to the need for fuel efficient vehicles due to the rise in their acceptance in the market and general performance relative to other alternative powertrain configurations, such as electric vehicles.
A driver's perceived vehicle quality is based in part on its drivability. Thus, increasing the drivability of HEVs would likely further improve consumer acceptance and utilization of HEVs. The drivability of a vehicle includes various performance metrics, such as acceleration and gradeability, as well as the frequency of unwanted behavior within the powertrain, which includes noise, vibrations, and harshness issues. Drivability and fuel economy of HEVs are competing goals because there is typically a trade-off between these two objectives; therefore, it is imperative that any method used to improve drivability does not negatively impact fuel economy.
One source of drivability issues in HEVs is the restart of the internal combustion engine (ICE) after a period in which the vehicle is in a pure electric drive mode. Similarly, the restart of the ICE in vehicles equipped with a stop-start features may also present a drivability issue.
Existing approaches have focused on altering the supervisory controller using optimal control algorithms, such as shortest-path stochastic dynamic programming (SP-SDP) or deterministic dynamic programming (DDP), or implementing feedback control strategies for the supervisory controller and/or lower level control systems. These control strategies significantly add to the vehicle controller complexity and require substantial tuning for each HEV platform.
It is with respect to these and other considerations that various embodiments of the present invention are presented herein.